U.S. patent number 7,999,144 [Application Number 11/469,847] was granted by the patent office on 2011-08-16 for microchannel apparatus and methods of conducting catalyzed oxidative dehydrogenation.
This patent grant is currently assigned to Velocys. Invention is credited to Ravi Arora, Francis P. Daly, Amanda Glass, Richard Long, Terry Mazanec, Paul W. Neagle, Steven T. Perry, Anna Lee Tonkovich, Bin Yang, Thomas D. Yuschak.
United States Patent |
7,999,144 |
Tonkovich , et al. |
August 16, 2011 |
Microchannel apparatus and methods of conducting catalyzed
oxidative dehydrogenation
Abstract
Methods of oxidative dehydrogenation are described.
Surprisingly, Pd and Au alloys of Pt have been discovered to be
superior for oxidative dehydrogenation in microchannels. Methods of
forming these catalysts via an electroless plating methodology are
also described. An apparatus design that minimizes heat transfer to
the apparatus' exterior is also described.
Inventors: |
Tonkovich; Anna Lee (Dublin,
OH), Yang; Bin (Columbus, OH), Perry; Steven T.
(Galloway, OH), Mazanec; Terry (Solon, OH), Arora;
Ravi (New Albany, OH), Daly; Francis P. (Delaware,
OH), Long; Richard (New Albany, OH), Yuschak; Thomas
D. (Lewis Center, OH), Neagle; Paul W. (Westerville,
OH), Glass; Amanda (Galloway, OH) |
Assignee: |
Velocys (Plain City,
OH)
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Family
ID: |
39152706 |
Appl.
No.: |
11/469,847 |
Filed: |
September 1, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080058574 A1 |
Mar 6, 2008 |
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Current U.S.
Class: |
585/658; 585/444;
585/443; 585/440; 585/654; 585/435; 422/601; 422/603; 585/660;
585/659; 585/441; 585/656 |
Current CPC
Class: |
C01B
3/50 (20130101); C01B 3/386 (20130101); B01J
19/0093 (20130101); C07C 5/48 (20130101); C07C
5/48 (20130101); C07C 11/04 (20130101); B01J
2219/00824 (20130101); B01J 2219/00822 (20130101); C01B
2203/0261 (20130101); C01B 2203/1035 (20130101); C07C
2523/52 (20130101); B01J 2219/00873 (20130101); C01B
2203/1041 (20130101); C01B 2203/107 (20130101); C07C
2523/44 (20130101); B01J 2219/00984 (20130101); C01B
2203/1064 (20130101); B01J 2219/0086 (20130101); C01B
2203/1247 (20130101); C07C 2523/42 (20130101); B01J
2219/00788 (20130101); B01J 2219/00869 (20130101); C01B
2203/048 (20130101); B01J 2219/00783 (20130101); B01J
2219/00835 (20130101); C01B 2203/04 (20130101); B01J
2219/00891 (20130101) |
Current International
Class: |
C07C
5/32 (20060101) |
Field of
Search: |
;585/658,654,656 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 01/12312 |
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Feb 2001 |
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WO |
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WO 01/54807 |
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Aug 2001 |
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WO |
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WO 2004108639 |
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Dec 2004 |
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WO |
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Other References
PCT Written Opinion in PCT/US2005/009814, mailed Oct. 5, 2006.
cited by other .
Bhasin et al., "Dehydrogenation and oxydehydrogenation of paraffins
to olefins," Appl. Catal. A, Gen. 221 (2001) 397-419. cited by
other .
Wolfrath et al., "Novel Membrane Reactor with Filamentous Catalytic
Bed for Propane Dehydrogenation," Ind. Eng. Chem. Res. 2001, 40.
5234-5239. cited by other .
Kestenbaum et al., "Synthesis of ethylene oxide in a microreaction
system," in IMRET 3 Proceedings of the Third international Conf. on
Microreaction Technology 207-212 (1999). cited by other .
Beretta et al., "Production of olefins via oxidative
dehydrogenation of light paraffins at short contact times,"
Catalysis Today, 64, pp. 103-111 (2001). cited by other .
Steinfeldt et al., "Comparative studies of the oxidative
dehydrogenation of propane in micro-channels reactor module and
fixed-bed reactor," Studies in Surface Science and Catalysis, pp.
185-190 (2001). cited by other .
Claus et al., "Miniaturization of screening devices for the
combinatorial development of heterogensous catalysts," Catalysis
Today, 67, pp. 319-339 (2001). cited by other.
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Primary Examiner: Caldarola; Glenn A
Assistant Examiner: Etherton; Bradley
Attorney, Agent or Firm: Rosenberg; Frank
Government Interests
GOVERNMENT RIGHTS
This invention was made with Government support under contract #
DE-FC36-04GO14154 awarded by the United States Department of
Energy. The government has certain rights in the invention.
Claims
We claim:
1. A method for oxidatively dehydrogenating a hydrocarbon,
comprising: passing a process stream comprising an oxygen source
and a hydrocarbon into a microchannel in a first section of a
microchannel reactor, wherein, in the first section, the oxygen
reacts with a fuel to generate heat; flowing the process stream
through a u-bend and into a second section; wherein the process
stream in the first section and a process stream in a second
section are separated by a thermally conductive wall; wherein heat
from the reaction with oxygen in the first section passes through
the thermally conductive wall and into the process stream in the
second section; and removing hydrogen from the hydrocarbon to form
a product and hydrogen; and wherein more of the product is formed
in the second section than in the first section.
2. The method of claim 1 wherein hydrocarbon conversion in the
first section is 30% or less.
3. The method of claim 1 wherein the product is formed with an
overall conversion of at least 70% and an overall selectivity of
80%, and wherein contact time of the process stream in the
microchannel reactor is 100 ms or less.
4. The method of claim 3 wherein the peak temperature is
1050.degree. C. or less.
5. The method of claim 3 wherein the peak temperature is
1000.degree. C. or less.
6. The method of claim 1 wherein the first section, in a region
where the oxygen source reacts with the fuel to generate heat,
comprises a first cross-sectional area; wherein the second section
comprises a second cross-sectional area; and wherein the second
cross sectional area is at least twice as large as the first
cross-sectional area.
7. The method of claim 1 wherein the hydrocarbon is selected from
the group of ethane, propane and isobutane; wherein hydrogen flows
into the first section; wherein the oxygen source comprises
dioxygen; and wherein at least 99% of the dioxygen is consumed in
the first section.
8. A method for oxidatively dehydrogenating a hydrocarbon,
comprising: passing a process stream comprising an oxygen source
and a hydrocarbon into a microchannel in a first section of a
microchannel reactor, wherein, in the first section, the oxygen
reacts with a fuel to generate heat; flowing the feed stream
through a u-bend and into a second section; wherein the first
section, in a region where the oxygen source reacts with the fuel
to generate heat, comprises a first cross-sectional area; wherein
the process stream in the first section and a process stream in a
second section are separated by a thermally conductive wall;
wherein heat from the reaction with oxygen in the first section
passes through the thermally conductive wall and into the process
stream in the second section; and in the second section, the
hydrocarbon reacts to form a product and hydrogen; wherein the
second section comprises a second cross-sectional area; and wherein
the second cross sectional area is at least twice as large as the
first cross-sectional area.
9. The method of claim 8 wherein at least 70% of the hydrocarbon is
converted, and the selectivity to an alkene or aralkene is at least
80%; and wherein the flow rate is controlled so that the contact
time of the process stream is 100 ms or less.
10. The method of claim 9 wherein the first section, u-bend and
second section each comprise an unobstructed bulk flow path.
11. The method of claim 9 wherein the first section comprises a
wall coating of a Pt alloy catalyst; wherein the alloy catalyst
further comprises Au or Pd; and wherein the levels of hydrocarbon
conversion and selectivity are maintained for at least 100 hours of
continuous operation without regeneration.
12. The method of claim 8 wherein more of the product is formed in
the second section than in the first section.
13. The method of claim 8 wherein the first section comprises a
wall coating of a Pt alloy catalyst; wherein the alloy catalyst
further comprises Au or Pd.
14. The method of claim 8 wherein the second cross sectional area
is at least three times as large as the first cross-sectional area;
and wherein a flow path is continuous through the first section,
into and through the u-bend and into and through the second
section; wherein the continuous flow path comprises a transitional
region from the first cross-sectional area to the second
cross-sectional area, wherein the transitional region comprises an
increasing cross-sectional area that increases in cross-sectional
area from the first cross-sectional area to the second
cross-sectional area, and the transitional region does not contain
any region in which the flow path increases in cross-sectional area
by three times or more over a length less than 0.6 cm, except that,
if the transitional region includes a u-bend, there can be a region
within 1 cm of the u-bend in which the flow path increases in
cross-sectional area by three times or more over a length less than
0.6 cm.
15. A method for oxidatively dehydrogenating a hydrocarbon,
comprising: passing a process stream comprising an oxygen source
and a hydrocarbon into a microchannel in a first section of a
microchannel reactor, wherein the microchannel reactor comprises a
continuous flow path through the first section, into and through a
second section; wherein, in the first section, the oxygen source
reacts with a fuel to generate heat; wherein the first section, in
a region where the oxygen source reacts with the fuel to generate
heat, comprises a first cross-sectional area; passing the process
stream from the first section into the second section; wherein, in
the second section, the hydrocarbon reacts to form an alkene or
aralkene and hydrogen; wherein the second section comprises a
second cross-sectional area; wherein the second cross sectional
area is at least three times as large as the first cross-sectional
area; and wherein the continuous flow path comprises a transitional
region from the first cross-sectional area to the second
cross-sectional area, wherein the transitional region comprises an
increasing cross-sectional area that increases in cross-sectional
area from the first cross-sectional area to the second
cross-sectional area, and the transitional region does not contain
any region in which the flow path increases in cross-sectional area
by three times or more over a length less than 0.6 cm, except that,
if the transitional region includes a u-bend, there can be a region
within 1 cm of the u-bend in which the flow path increases in
cross-sectional area by three times or more over a length less than
0.6 cm.
16. The method of claim 15 wherein the process stream is
essentially without diluents.
17. The method of claim 15 wherein the transitional region includes
a u-bend, and wherein there is a region within 1 cm of the u-bend
in which the flow path increases in cross-sectional area by three
times or more over a length less than 0.6 cm.
18. The method of claim 15 wherein the transitional region does not
contain any region in which the flow path increases in
cross-sectional area by three times or more over a length less than
0.6 cm.
19. A method for oxidatively dehydrogenating a hydrocarbon,
comprising: passing a process stream comprising an oxygen source
and a hydrocarbon into one of the at least two flow paths of
apparatus comprising: a processor body having a length and
comprising a central axis and at least two flow paths along a
length of the processor body and radiating out from the center axis
wherein, in a direction perpendicular to length, each of the at
least two flow paths have a cross section that is substantially
rectangular; and further wherein the one of the at least two flow
paths comprises an ODH catalyst.
20. The method of claim 19 further comprising a ubend in the
apparatus so that the process stream returns in the same direction
it came.
21. A method for oxidatively dehydrogenating a hydrocarbon,
comprising: passing a process stream comprising an oxygen source
and a hydrocarbon into a microchannel in a first section of a
microchannel reactor, wherein, in the first section, the oxygen
source reacts with a fuel source to generate heat; flowing the feed
stream through a u-bend and into a second section; wherein the
first section comprises a Pt alloy catalyst wherein the Pt alloy
comprises Au or Pd as an alloying element; wherein the process
stream in the first section and a process stream in a second
section are separated by a thermally conductive wall; wherein heat
from the reaction with oxygen in the first section passes through
the thermally conductive wall and into the process stream in the
second section; and in the second section, removing hydrogen from
the hydrocarbon to form a product and hydrogen.
22. The method of claim 21 wherein the Pt alloy catalyst is an
electrolessly applied wall coating.
23. The method of claim 21 wherein the first section, in a region
where the oxygen source reacts with the fuel to generate heat,
comprises a first cross-sectional area; wherein the second section
comprises a second cross-sectional area; and wherein the second
cross sectional area is at least twice as large as the first
cross-sectional area.
24. The method of claim 23 wherein the second cross sectional area
is at least three times as large as the first cross-sectional area;
and wherein a flow path is continuous through the first section,
into and through the u-bend and into and through the second
section; and wherein the continuous flow path comprises a
transitional region from the first cross-sectional area to the
second cross-sectional area, wherein the transitional region
comprises an increasing cross-sectional area that increases in
cross-sectional area from the first cross-sectional area to the
second cross-sectional area, and the transitional region does not
contain any region in which the flow path increases in
cross-sectional area by three times or more over a length less than
0.6 cm, except that, if the transitional region includes a u-bend,
there can be a region within 1 cm of the u-bend in which the flow
path increases in cross-sectional area by three times or more over
a length less than 0.6 cm.
25. A method for oxidatively dehydrogenating a hydrocarbon,
comprising: passing an oxygen source and a hydrocarbon into a
microchannel at a temperature of at least 850.degree. C.; wherein
the microchannel comprises an electroless plating of a Pt alloy
catalyst wherein the Pt alloy comprises Au or Pd as an alloying
element; controlling flow rate such that the contact time is 100 ms
or less; wherein at least 70% of the hydrocarbon is converted to
products and wherein selectivity to alkene or aralkene is at least
80%; and maintaining conversion and selectivity at these levels for
at least 100 hours without performing a decoking step or a catalyst
regeneration step.
26. The method of claim 25 wherein the peak temperature is
1050.degree. C. or less.
27. The method of claim 25 wherein the Pt alloy catalyst comprises
Au as an alloying element.
28. The method of claim 25 wherein the hydrocarbon consists
essentially of ethane, and wherein hydrogen gas also flows through
the microchannel.
29. The method of claim 28 wherein the hydrocarbon conversion is at
least about 77%.
30. The method of claim 25 wherein the hydrocarbon conversion is at
least about 80%.
Description
BACKGROUND OF THE INVENTION
Oxidative dehydrogenation (ODH) has for a long period been a topic
on intense academic and industrial interest due to its potential
for economically producing olefins. One promising route to
oxidative dehydrogenation is by utilizing the advantages provided
by microchannel technology. Pioneering work in designing
microchannel systems for oxidative dehydrogenation is described in
U.S. Published Patent Application No. 2004/0034266 by Brophy et
al., and this published application is incorporated herein as if
reproduced in full below. Improved catalyst formulations and
methods for conducting ODH in microchannels are described in U.S.
Published Patent Application No. 20050272965, published Dec. 8,
2005; this published application is also incorporated herein as if
reproduced in full below.
Numerous types of conventional apparatus have been proposed for
conducting ODH reactions including monoliths, fixed beds and
fluidized beds. Lodeng et al. in U.S. Pat. No. 5,997,826 describe a
reaction in which relatively narrow, catalyst-free oxygen mixing
zones alternate with relatively larger catalyst-containing ODH
zones.
Pt and some Pt alloys have long been known as catalysts for some
applications in high temperature oxidative dehydrogenation. For
example, Font Freide et al. in U.S. Pat. No. 4,940,826 discuss Pt
and Pt--Pd catalysts for the oxidative dehydrogenation of ethane,
propane and butane. U.S. Pat. Nos. 5,639,929 and 6,846,773 report
the use of Pt--Au catalyst particles in fluidized bed reactors,
although in the '773 patent it is mentioned that a Pt--Au monolith
catalyst could not initiate ethane ODH. Although several patents
broadly discuss a broad range of Pt catalysts; recent work have
focused on Pt--Sn and Pt--Cu as the best catalysts for ODH. See
U.S. Pat. Nos. 6,166,283, 6,365,543, 6,566,573, 6,756,515, and
6,756,340. Indeed, Schmidt et al. (see, for example, U.S. Pat. No.
6,452,061) have warned against Pd or Au alloys with Pt because
these alloys are detrimental to the results of the ODH process.
SUMMARY OF THE INVENTION
The invention provides novel methods of oxidatively dehydrogenating
a hydrocarbon. Novel apparatus and systems are also disclosed.
In a first aspect, the invention provides a method for oxidatively
dehydrogenating a hydrocarbon, comprising: passing a an oxygen
source and a hydrocarbon into a microchannel at a temperature of at
least 850.degree. C. The microchannel comprises an electroless
plating of a Pt alloy catalyst wherein the Pt alloy comprises Au or
Pd as an alloying element. In this method, the flow rate is
controlled such that the contact time is 100 ms or less. In this
method, at least 70% of the hydrocarbon is converted to products,
selectivity to alkene or aralkene is at least 80%; and conversion
and selectivity are maintained above these levels for at least 100
hours without performing a decoking step or a catalyst regeneration
step.
In another aspect, the invention provides a method for oxidatively
dehydrogenating a hydrocarbon, comprising: passing a process stream
comprising an oxygen source and a hydrocarbon into a microchannel
in a first section of a microchannel reactor, wherein, in the first
section, the oxygen reacts with a fuel to generate heat; flowing
the feed stream through a u-bend and into a second section; wherein
the first section, in a region where the oxygen source reacts with
the fuel to generate heat, comprises a first cross-sectional area;
wherein the process stream in the first section and a process
stream in a second section are separated by a thermally conductive
wall; wherein heat from the reaction with oxygen in the first
section passes through the thermally conductive wall and into the
process stream in the second section; and, in the second section,
removing hydrogen from the hydrocarbon to form a product and
hydrogen; wherein the second section comprises a second
cross-sectional area; and wherein the second cross sectional area
is at least twice as large as the first cross-sectional area.
In a further aspect, the invention provides a method for
oxidatively dehydrogenating a hydrocarbon, comprising: passing a
process stream comprising an oxygen source and a hydrocarbon into a
microchannel in a first section of a microchannel reactor, wherein
the microchannel reactor comprises a continuous flow path through
the first section, into and through a second section; wherein, in
the first section, the oxygen source reacts with a fuel to generate
heat; wherein the first section, in a region where the oxygen
source reacts with the fuel to generate heat, includes a first
cross-sectional area. The process stream passes from the first
section into the second section; and, in the second section, the
hydrocarbon reacts to form an alkene or aralkene and hydrogen;
wherein the second section comprises a second cross-sectional area.
In this method, the second cross sectional area is at least three
times as large as the first cross-sectional area; and the
continuous flow path comprises a transitional region from the first
cross-sectional area to the second cross-sectional area, wherein
the transitional region comprises an increasing cross-sectional
area that increases in cross-sectional area from the first
cross-sectional area to the second cross-sectional area, and the
transitional region does not contain any region in which the flow
path increases in cross-sectional area by three times or more over
a length less than 0.6 cm, except that, if the transitional region
includes a u-bend, there can be a region within 1 cm of the u-bend
in which the flow path increases in cross-sectional area by three
times or more over a length less than 0.6 cm. By use of this
method, coking in the reactor can be eliminated or greatly
reduced.
In yet another aspect, the invention provides chemical processing
apparatus, comprising: a processor body having a length and
comprising a central axis and at least two flow paths along a
length of the processor body and radiating out from the center
axis; wherein, in a direction perpendicular to length, each of the
at least two flow paths have a cross section that is substantially
rectangular. Here "radiating out" does not mean that the paths
necessarily touch the center axis, only that the width of the paths
project in a radial direction away from the central axis. "Length"
is perpendicular to width and length of the processor body is
defined to be in same direction as the length of the flow paths
which are substantially straight. The invention also includes a
method using this apparatus to conduct one or more unit operations
in the flow paths. A preferred unit operation is ODH. Preferably,
the processor body is cylindrical.
In a further aspect, the invention provides a method for
oxidatively dehydrogenating a hydrocarbon, comprising: passing a
process stream comprising an oxygen source and a hydrocarbon into a
microchannel in a first section of a microchannel reactor, wherein,
in the first section, the oxygen source reacts with a fuel to
generate heat. The first section includes a Pt alloy catalyst that
comprises Au or Pd as an alloying element. The process stream flows
through a u-bend and into a second section. The process stream in
the first section and a process stream in a second section are
separated by a thermally conductive wall. Heat from the reaction
with oxygen in the first section passes through the thermally
conductive wall and into the process stream in the second section;
and, in the second section, the hydrocarbon reacts to form a
product and hydrogen. In this method, heat from the oxidation
reaction typically passes into the product (second) section by both
convection and conduction through the thermally conductive
wall.
In another aspect, the invention provides a method for oxidatively
dehydrogenating a hydrocarbon, comprising: passing a process stream
comprising an oxygen source and a hydrocarbon into a microchannel
in a first section of a microchannel reactor, wherein, in the first
section, the oxygen source reacts with a fuel to generate heat. The
process stream flows through a u-bend and into a second section.
The process stream in the first section and a process stream in a
second section are separated by a thermally conductive wall; and
heat generated by the reaction of fuel with the oxygen source in
the first section passes through the thermally conductive wall and
into the process stream in the second section. In the second
section, the hydrocarbon reacts to form a product and hydrogen. In
this method, more of the product (alkene or aralkene) is formed in
the second section than in the first section.
The invention also includes catalysts comprising a Pt alloy
disposed on a substrate, where the Pt alloy comprises Pt alloyed
with Pd and/or Au. Preferably, the Pt alloy is formed by
electroless plating--the electroless plating technique yields a
unique structure that is not obtained with other techniques.
Preferably the substrate comprises an aluminide layer. The catalyst
may additionally be characterized by any of the properties
(including reactive properties) disclosed in the specification or
examples. For example, the catalyst can be characterized as
possessing an activity such that, when exposed to the conditions of
example 1 (or any of the other examples), at 902.degree. C., there
is an ethane conversion of at least 70%, preferably at least 75%,
and a selectivity of at least 80% for at least 100 hours.
The invention further includes any of the apparatus described here.
In particular, the invention includes any of the apparatus
described in conjunction with the inventive methods. Any of the
devices described here will often be integrated within a larger
device. For example, the process channel will typically include a
run up length in which there is little or no reaction occurs (which
could be due to low temperature or lack of an oxygen source); and
the run up length of the process channel is adjacent to an extended
length of product channel. In this region, which is prior to the
first section where oxidation occurs and typically after the
majority of the second section where dehydrogenation occurs, there
is thermal transfer from the hot product stream to the cooler
process stream in the run up to the oxidation section.
The invention also includes systems having the characteristics
described herein. Systems of the invention can be described as
including apparatus and/or catalyst in combination with reactants
and/or products. Optionally, systems can be further characterized
by the conditions at which they operate.
GLOSSARY
In some preferred embodiments, the internal surfaces have been
coated with a metal aluminide, which is typically itself coated
with one or more layers, such as a catalyst layer. "Metal
aluminide" refers to a metallic material containing 10% or more
Metal and 5%, more preferably 10%, or greater Aluminum (Al) with
the sum of Metal and Al being 50% or more. These percentages refer
to mass percents. Preferably, a metal aluminide contains 50% or
more metal and 10% or greater Al with the sum of Ni and Al being
80% or more. In embodiments in which Metal and Al have undergone
significant thermal diffusion, it is expected that the the
composition of a Metal-Al layer will vary gradually as a function
of thickness so that there may not be a distinct line separating
the Metal-Al layer from an underlying Metal-containing alloy
substrate. A preferred metal aluminide is nickel aluminide (NiAl).
"Nickel aluminide" refers to a material containing 10% or more Ni
and 10% or greater Al with the sum of Ni and Al being 50% or more.
These percentages refer to mass percents. Preferably, a nickel
aluminide contains 20% or more Ni and 10% or greater Al with the
sum of Ni and Al being 80% or more. In embodiments in which Ni and
Al have undergone significant thermal diffusion, it is expected
that the composition of a Ni--Al layer will vary gradually as a
function of thickness so that there may not be a distinct line
separating the Ni--Al layer from an underlying Ni-based alloy
substrate. Microchannel apparatus having metal aluminide coatings
are described elsewhere, and, therefore, they are not described in
detail here.
A "catalyst material" is a material that catalyzes a desired
reaction. It is not simply alumina. A catalyst material "disposed
over" a layer can be a physically separate layer (such as a
sol-deposited layer) or a catalyst material disposed within a
porous, catalyst support layer. "Disposed onto" or "disposed over"
mean directly on or indirectly on with intervening layers. In some
preferred embodiments, the catalyst material is directly on a
thermally-grown alumina layer, meaning without any intervening
layers.
A "catalyst metal" is the preferred form of catalyst material and
is a material in metallic form that catalyzes a desired
reaction.
A "chemical unit operation" comprises reactions, separations,
heating, cooling, vaporization, condensation, and mixing.
As is conventional patent terminology, "comprising" means including
and when this term is used the invention can, in some narrower
preferred embodiments, be described as "consisting essentially of"
or in the narrowest embodiments as "consisting of." Aspects of the
invention described as "comprising a" are not intended to be
limited to a single component, but may contain additional
components. Compositions "consisting essentially of" a set of
components allow other components that so not substantially affect
the character of the invention, and, similarly, compositions that
are "essentially" without a specified element do not contain
amounts of the element as would substantially affect the desired
properties. In place of "comprising", any of the terms "consists
of" or "consists essentially of", may alternatively be used to
describe more limited aspects of the invention.
Unless stated otherwise, "conversion percent" refers to absolute
conversion percent throughout these descriptions. "Contact time" is
defined as the total catalyst chamber volume (including the
catalyst substrate volume) divided by the total volumetric inlet
flowrate of reactants at standard temperature and pressure (STP:
273K and 1.013 bar absolute). Catalyst chamber volume includes any
volume between a catalyst coating (or other flow-by catalyst
arrangement) and the opposite wall of a reaction channel.
In preferred embodiments, an electroless coating is contiguous over
at least 1 cm, more preferably at least 5 cm, of a
microchannel.
The phrase a "coating grows away from the wall" refers to the
direction that a coating grows--either by thermal oxidation or an
accretion process such as electroless plating.
A "contiguous microchannel" is a microchannel enclosed by a
microchannel wall or walls without substantial breaks or
openings--meaning that openings (if present) amount to no more than
20% (in some embodiments no more than 5%, and in some embodiments
without any openings) of the area of the microchannel wall or walls
on which the opening(s) are present.
"Directly disposed" means that a material is directly applied to a
specified layer. There is not an intervening washcoating, nor is
the material codeposited with a washcoated catalyst support.
"Directly deposited" has the same meaning. The inventive method is
very flexible, an electroless catalyst layer can be directly
deposited electrolessly on any of the substrates mentioned
herein.
"Hydrocarbon" is any alkane or aralkane containing from 2 to 20
carbon atoms.
An "interior microchannel" is a microchannel within a device that
is surrounded on all sides by a microchannel wall or walls except
for inlets and outlets, and, optionally, connecting holes along the
length of a microchannel such as a porous partition or orifices
such as connecting orifices between a fuel channel and an oxidant
channel. Since it is surrounded by walls, it is not accessible by
conventional lithography, conventional physical vapor deposition,
or other surface techniques.
An "insert" is a component that can be inserted into a channel.
A "manifold" is a header or footer that connects plural
microchannels and is integral with the apparatus.
Measurement techniques--For all coatings, "average thickness" can
be measured by cross-sectional microscopy (obtained by cutting open
a microchannel device) or, for coatings that are about 5 .mu.m
thick or less, by EDS elemental analysis. In the case of channels
connected to a common manifold or otherwise connected to be filled
from the same inlet, the "average thickness" is averaged over all
the channels, or for a large number of connected channels, at least
10 channels selected to fairly represent the totality of the
connected channels. Measurements should be made over the entire
length of a continguous coating; that is, not just for 1 cm
selected out of a larger contiguous coating. "Coating loading" is
measured the same as average thickness except that height and/or
thickness (or elemental analysis) of the coating is measured to get
a volume or mass. Unless specified as a corner measurment, average
coating thickness should be measured along the center line between
corners (if present), and any set of corners can be selected.
Corner thickness can be measured on a single corner; however, the
corner must be representative (not an aberration).
A "microchannel" is a channel having at least one internal
dimension (wall-to-wall, not counting catalyst) of 1 cm or less,
preferably 2 mm or less (in some embodiments about 1.0 mm or less)
and greater than 100 nm (preferably greater than 1 .mu.m), and in
some embodiments 50 to 500 .mu.m. Microchannels are also defined by
the presence of at least one inlet that is distinct from at least
one outlet. Microchannels are not merely channels through zeolites
or mesoporous materials. The length of a microchannel corresponds
to the direction of flow through the microchannel. Microchannel
height and width are substantially perpendicular to the direction
of flow of through the channel. In the case of a laminated device
where a microchannel has two major surfaces (for example, surfaces
formed by stacked and bonded sheets), the height is the distance
from major surface to major surface and width is perpendicular to
height.
"Ni-based" alloys are those alloys comprising at least 30%,
preferably at least 45% Ni, more preferably at least 60% (by mass).
In some preferred embodiments, these alloys also contain at least
5%, preferably at least 10% Cr.
A "post-assembly" coating is applied onto three dimensional
microchannel apparatus. This is either after a laminating step in a
multilayer device made by laminating sheets or after manufacture of
a manufactured multi-level apparatus such as an apparatus in which
microchannels are drilled into a block. This "post-assembly"
coating can be contrasted with apparatus made by processes in which
sheets are coated and then assembled and bonded. The post-assembly
coating provides advantages such as crack-filling and ease of
manufacture. Additionally, a coating could interfere with diffusion
bonding of a stack of coated sheets and result in an inferior bond.
Whether an apparatus is made by a post-assembly coating is
detectable by observable characteristics such as gap-filling,
crack-filling, elemental analysis (for example, elemental
composition of sheet surfaces versus bonded areas). Typically,
these characteristics are observed by optical microscopy, electron
microscopy or electron microscopy in conjunction with elemental
analysis. Thus, for a given apparatus, there is a difference
between pre-assembled and post-assembled coated devices, and an
analysis using well-known analytical techniques can establish
whether a coating was applied before or after assembly (or
manufacture in the case of drilled microchannels) of the
microchannel device. In preferred embodiments, an electroless
plating is applied post-assembly.
"Unit operation" means chemical reaction, vaporization,
compression, chemical separation, distillation, condensation,
mixing, heating, or cooling. A "unit operation" does not mean
merely fluid transport, although transport frequently occurs along
with unit operations. In some preferred embodiments, a unit
operation is not merely mixing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional (cut away) view of apparatus for ODH
that was modeled in the Examples section.
FIG. 2 is a top down view of the sheet containing the oxygen
subchannels. Jet holes for passage of the oxygen into the process
channel (i.e., the first section). A fuel is oxidized in the
process channel to generate heat for the dehydrogenation
reaction.
FIG. 3 shows a cross-sectional view of the region near the u-bend
and illustrates how shim construction methods could be used to make
steps for increasing volume of the product channel. The process
stream flow path is shaded in this figure.
FIG. 4 is a schematic representation of heat transfer in a u-bend
device.
FIG. 5a schematically illustrates a simple u-bend. In this
illustration, a catalyst (shaded region) is disposed on surfaces in
and near the u-bend.
FIG. 5b schematically illustrates a u-bend modified by the addition
of baffles for more surface area.
FIG. 6a-c shows an embodiment of apparatus that minimizes heat
transfer to the exterior of the device. FIG. 6a shows, in
cross-section, the flow path slots. FIG. 6b is a cut away view of a
u-bend.
FIG. 6c is a scaled up device with multiple units.
FIG. 7 is a graph from the model calculations showing temperature
as a function of length for the type of device illustrated in FIGS.
1-2.
FIG. 8 shows structures that modify manifolding to equalize flow
across multiple channels.
FIG. 9 is a figure labeling domains discussed in the examples.
FIG. 10 are graphs from the model calculations showing temperature
as a function of length for the devices described in the
examples.
FIG. 11 shows the mass fraction of ethane in the first (process)
and second (product) sections of a u-bend reactor.
FIG. 12 shows reactor designs with a completely open product
channel (black) and a product channel modified with support ribs
(white), as explained in the examples.
FIG. 13 are graphs from the model calculations showing temperature
as a function of length for the devices described in the
examples.
DETAILED DESCRIPTION OF THE INVENTION
Catalysts
As is known, an electroless plating solution comprises a metal
compound and a reducing chemical. A complexing agent may be added
to prevent reduction of the metal ions in solution. In some
embodiments, the reduction process may be catalyzed by a small
amount of catalytic metal ions. Preferred metals for the
electroless deposition include Cu, Au, Pd, Pt, Sn and combinations
thereof. After plating, the residual solution could be drained
out.
The use of electroless plating of catalytic metals on reactor
walls, both conductive and non-conductive, can be used to create a
uniform metal coating inside a channel. Such an electroless plating
solution could comprise a water soluble metal salt, a reducing
agent such as hydrazine hydrate, possibly a stabilizer such as EDTA
to prevent precipitation of the plating metal, optionally an
accelerator such as 3,4-dimethoxybenzoic acid or an acid such as
acetic acid to adjust the pH for optimum plating. For a
microchannel reactor the electroless plating solution is preferably
filled (to the desired height) within the channels prior to the
initiation of the reaction. Pressure can be applied during filling
to control fill height in selected channels. The solution could be
introduced at room temperature or below and then heated to the
requisite plating temperature. In some applications it may be
important that the plating process end before the plating solution
is drained, particularly if the draining process is long relative
to the plating process, to achieve a uniform coating. This can be
accomplished by, for example, controlling a plating
composition/reaction in which one of the essential reactants is
depleted before the draining process begins. Another approach would
be to reduce the plating temperature prior to draining. For
example, in addition to the draining issues, the plating liquid
should be selected to be stable in microchannels so that particles
will not form in solution and drift by gravity.
In this invention, we have found that the Pt alloys (e.g., Pt--Cu,
Pt--Au and Pt--Pd) prepared with electroless plating exhibit
surprisingly superior ODH performance. The superior performance may
be due to better coating uniformity and better heat transfer. For
electroless plating of alloys, the substrates could be plated with
Pt first, or another metal first, or two or more metals
simultaneously. The Pt/metal ratio and total loading could be
controlled by plating conditions, such as temperature, solution
concentration, and plating time. Preferred Pt alloys could include
Pt--Cu, Pt--Au, Pt--Ag, Pt--Pd, Pt--Fe, Pt--Co, Pt--Ni, and
combinations thereof. Additional promoters, stabilizing materials,
or chemical modifiers, or combinations of these could be included.
Examples of these include transition metal ions especially Group 8
ions, alkali or alkaline earth elements, lanthanides or rare earth
elements, or combinations of these. These additional materials
could be added before or after the precious metals. After Pt and
metal plating, the catalysts could be heat-treated at high
temperatures to form Pt alloys. The heat-treating atmosphere could
be oxidizing, reducing, or inert atmosphere or in vacuum.
The metal content in a catalyst or other article can be described
either in terms of weight percent or in terms of mass per geometric
surface area of substrate. Weight percent is based on the weight of
platinum (in preferred ODH catalysts) as a percent of catalyst
powder, catalyst pellets, or washcoat; it does not include the
weight of an underlying substrate and does not include the weight
of interlayers between a washcoat (or washcoats) and an underlying
substrate. For example, in the case of an alloy felt washcoated
with alumina and Pt, the weight % would be
Pt/(Pt+Al.sub.2O.sub.3).times.100%. For a metal coupon that has
been aluminized, then oxidized, then treated with solution of
alumina and lanthanum and Pt, the weight of the oxidized aluminized
layer would not be included in the calculation of weight % Pt.
For flat or substantially flat substrates (such as a flat
microchannel wall), a coating can be characterized by the amount of
desired material on a geometric surface area; that is, an area that
can be measured with a ruler. For purposes of the present
invention, a microchannel wall with embedded surface features is
considered a substantially flat surface. In some preferred
embodiments, the catalyst contains at least 0.3 mg/cm.sup.2 Pt, in
some preferred embodiments at least 0.6 mg/cm.sup.2 Pt, and in some
embodiments 0.2 to 2 mg/cm.sup.2 Pt. For purposes of this
measurement, the area refers to the geometrical area of the
substrate; for a flat surface such as a foil or coupon, this area
is quite simple, for a honeycomb or finned substrate or reaction
channel, it would include all the surfaces that are coated by
catalyst. The weight percent of Pt can be determined by known
methods of chemical analysis.
Preferred catalyst compositions comprise Pt alloyed with Au and/or
Pd. The effectiveness of these catalysts was surprising in view of
the prior art teachings that these alloys would be plagued by
coking problems. Gold (Au), if present, is preferably present in a
Pt:Au ratio of 10:1 to 0.5:1, more preferably about 3:1 to about
1:1, more preferably 2.5:1 to 1.5:1, and in some embodiments about
2:1. Palladium (Pd), if present, is preferably in the present in a
Pt:Au ratio of up to about 10:1, more preferably 5:1 to 0.5:1, and
still more preferably 1.5:1 to 0.5:1, and in some embodiments about
1:1. Gold is superior to tin because it is less volatile.
Unless otherwise specified, elemental analyses of wall coatings
should be determined using energy dispersive spectroscopy (EDS) at
20 kV excitation energy (at 100.times., or if 100.times. is larger
than the area available, then the largest available area for SEM,
recognizing that some modifications may be required if such
measurement conditions are impracticable for particular systems).
As is well-known, this technique measures the surface composition,
as well as some thickness below the surface. Some catalysts of this
invention have a surface area, as measured by N.sub.2 adsorption
BET, of 10 m.sup.2/g or less, and in some embodiments a surface
area of 5 m.sup.2/g or less.
A catalyst coating can be applied to any support, including
pellets, foams and honeycombs, and, in preferred embodiments is
applied to a microchannel wall.
Thermally Grown Oxide
Prior to electroless plating, an oxide layer may be formed by
exposing a surface to an oxidizing atmosphere at elevated
temperature. In some preferred embodiments, a nickel aluminide or
platinum aluminide layer is oxidized. The thermally-grown oxide
layer is preferably 10 .mu.m thick or less, more preferably 1 .mu.m
thick or less, and in some embodiments is 0.2 .mu.m to 5 .mu.m
thick. Typically, these thicknesses are measured with an optical or
electron microscope. Generally, the thermally-grown oxide layer can
be visually identified; the underlying aluminide layer is metallic
in nature and contains no more than 5 wt % oxygen atoms; surface
washcoat layers may be distinguished from the thermally-grown oxide
by differences in density, porosity or crystal phase.
It should be recognized that the term "alumina" can be used to
refer to a material containing aluminum oxides in the presence of
additional metals. In the descriptions herein, unless specified,
the term "alumina" encompasses substantially pure material
("consists essentially of alumina") and/or aluminum oxides
containing modifiers.
Surface Features in Microchannel Walls
In some preferred embodiments, apparatus contains channels having
surface features to enhance fluid contact with a catalyst and/or
channel walls. Surface features are protrusions from or recesses
into a channel wall. If the area at the top of the features is the
same or exceeds the area at the base of the feature, then the
feature may be considered recessed. If the area at the base of the
feature exceeds the area at the top of the feature, then it may be
considered protruded. Surface features are described in detail in
U.S. patent application Ser. No. 11/388,792, filed Mar. 23, 2006,
which is incorporated herein as if reproduced in full below. The
staggered herringbone configuration is a particularly well-known
configuration for surface features.
Preferred ranges for surface feature depth (as defined as recessed
or protruded distance normal to the direction of flow through a
channel) are less than 2 mm. More preferrably less than 1 mm. In
some embodiments from 0.01 mm to 0.5 mm. The preferred range for
the width of the surface feature (as defined as the open distance
parallel to the direction of gravity) is less than 2 mm. More
preferrably less than 1 mm. In some embodiments from from 0.1 to
0.5 mm.
An advantage of electroless plating is that essentially uniform
coatings can be formed on surface features within a microchannel.
Measuring coating thickness can be performed ex situ by cutting the
device into cross sections and taking SEM photographs to
quantitatively measure the coating thickness.
Microchannel Apparatus
Microchannel reactors are characterized by the presence of at least
one reaction channel having at least one dimension (wall-to-wall,
not counting catalyst) of 1.0 cm or less, preferably 2.0 mm or less
(in some embodiments about 1.0 mm or less) and greater than 100 nm
(preferably greater than 1 .mu.m), and in some embodiments 50 to
500 .mu.m. A reaction channel is a channel containing a catalyst.
Microchannel apparatus is similarly characterized, except that a
catalyst-containing reaction channel is not required. Both height
and width are substantially perpendicular to the direction of flow
of reactants through the reactor. Microchannels are also defined by
the presence of at least one inlet that is distinct from at least
one outlet--microchannels are not merely channels through zeolites
or mesoporous materials. The height and/or width of a reaction
microchannel is preferably about 2 mm or less, and more preferably
1 mm or less. The length of a reaction channel is typically longer.
Preferably, the length of a reaction channel is greater than 1 cm,
in some embodiments greater than 20 cm, and in some embodiments in
the range of 1 to 100 cm. The sides of a microchannel are defined
by reaction channel walls. These walls are preferably made of a
hard material such as a ceramic, an iron based alloy such as steel,
or a Ni--, Co-- or Fe-based superalloy such as monel. The choice of
material for the walls of the reaction channel may depend on the
reaction for which the reactor is intended. In some embodiments,
the reaction chamber walls are comprised of a stainless steel or
Inconel.RTM. or other high temperatre alloy which is durable and
has good thermal conductivity. Typically, reaction channel walls
are formed of the material that provides the primary structural
support for the microchannel apparatus. Some microchannel apparatus
includes at least 10 layers laminated in a device, where each of
these layers contain at least 10 channels; the device may contain
other layers with less channels.
Microchannel reactors preferably include a plurality of
microchannel reaction channels and may also contain a plurality of
adjacent heat exchange microchannels. The plurality of microchannel
reaction channels may contain, for example, 2, 10, 100, 1000 or
more channels. In preferred embodiments, the microchannels are
arranged in parallel arrays of planar microchannels, for example,
at least 3 arrays of planar microchannels. In some preferred
embodiments, multiple microchannel inlets are connected to a common
header and/or multiple microchannel outlets are connected to a
common footer. Pressure drops can be low, allowing high throughput
and the catalyst can be fixed in a very accessible form within the
channels eliminating the need for separation. In some preferred
embodiments, a reaction microchannel (or microchannels) contains a
bulk flow path. The term "bulk flow path" refers to an open path
(contiguous bulk flow region) within the reaction chamber. A
contiguous bulk flow region allows rapid fluid flow through the
reaction chamber without large pressure drops. Bulk flow regions
within each reaction channel preferably have a cross-sectional area
of 5.times.10.sup.-8 to 1.times.10.sup.-2 m.sup.2, more preferably
5.times.10.sup.-7 to 1.times.10.sup.-4 m.sup.2. The bulk flow
regions preferably comprise at least 5%, more preferably at least
50% and in some embodiments, at least 90% of either 1) the internal
volume of the reaction chamber, or 2) a cross-section of the
reaction channel.
In many preferred embodiments, the microchannel apparatus contains
multiple microchannels, preferably groups of at least 5, more
preferably at least 10, parallel channels that are connected in a
common manifold that is integral to the device (not a
subsequently-attached tube) where the common manifold includes a
feature or features that tend to equalize flow through the channels
connected to the manifold. Examples of such manifolds are described
in U.S. Published Pat. Application No. 20050087767, filed Oct. 27,
2003 which is incorporated herein as if reproduced in full below.
In this context, "parallel" does not necessarily mean straight,
rather that the channels conform to each other. In some preferred
embodiments, a microchannel device includes at least three groups
of parallel microchannels wherein the channel within each group is
connected to a common manifold (for example, 4 groups of
microchannels and 4 manifolds) and preferably where each common
manifold includes a feature or features that tend to equalize flow
through the channels connected to the manifold.
While simple microchannels can be utilized, the invention has
advantages for apparatus with complex microchannel geometries. In
some preferred embodiments, the microchannel apparatus includes one
or more of the following characteristics: at least one contiguous
microchannel has a turn of at least 45.degree., in some embodiments
at least 90.degree., in some embodiments a u-bend, a length of 50
cm or more, or a length of 20 cm or more along with a dimension of
2 mm or less, and in some embodiments a length of 50-500 cm; at
least 2 adjacent channels, having an adjacent length of at least
one cm, are connected by plural orifices along a common
microchannel wall where the area of orifices amounts to 20% or less
of the area of the microchannel wall in which the orifices are
located and where each orifice is 0.6 mm.sup.2 or smaller, in some
embodiments 0.1 mm.sup.2 or smaller--this is a particularly
challenging configuration because a coating should be applied
without clogging the holes; or at least two, in some embodiments at
least 5, parallel microchannels having a length of at least 1 cm,
have openings to an integral manifold, where the manifold includes
at least one dimension that is no more than three times the minimum
dimension of the parallel microchannels (for example, if one of the
parallel microchannels had a height of 1 mm (as the smallest
dimension in the set of parallel microchannels), then the manifold
would possess a height of no more than 3 mm). An integral manifold
is part of the assembled device and is not a connecting tube. In
some apparatus, a microchannel contains a u-bend which means that,
during operation, flow (or at least a portion of the flow) passes
in opposite directions within a device and within a continguous
channel (note that a contiguous channel with a u-bend includes
split flows such as a w-bend, although in some preferred
embodiments all flow within a microchannel passes through the
u-bend and in the opposite direction in a single microchannel).
In preferred embodiments, the inventive apparatus (or method)
includes a catalyst material. In preferred embodiments, the surface
of the catalyst defines at least one wall of a bulk flow path
through which the mixture passes. During operation, a reactant
composition flows through the microchannel, past and in contact
with the catalyst. In some embodiments, a catalyst is provided as
an insert that can be inserted into (or removed from) each channel
in a single piece. The catalyst is preferably a coating of material
within a microchannel reaction channel or channels because it
creates an advantageous capacity/pressure drop relationship. In a
flow-by catalyst configuration, fluid preferably flows in a gap
adjacent to a porous insert or past a wall coating of catalyst that
contacts the microchannel wall.
In some preferred embodiments, microchannel apparatus for oxidative
dehydrogenation is essentially without heat exchange channels that
are separate from the process/product channels for the ODH process.
Examples are shown in FIGS. 1 and 2. As shown in FIG. 1, multiple
sets of microchannels can be provided within a single apparatus.
Preferably, the process stream in the process channel is fed into
the product channel.
In preferred embodiments of the present invention, there is a
u-turn in the ODH process channel. In this configuration, oxidation
can occur principally or entirely within the first side of the U.
Heat generated in the process side then transfers across a channel
wall to provide heat for the endothermic reaction that occurs in
the product side. This is schematically illustrated in FIG. 4. Of
course, some heat will also be convected along with the flow of the
process stream. Additionally, apparatus will typically also include
a recuperator section prior to the exothermic reaction section in
which heat from the product stream warms a fluid stream on its way
to the exothermic reaction (first) section.
Preferably, there is an ODH catalyst (not shown) in the first
section (labeled "Process Channel" in FIG. 1) of the u-bend
reactor. Pt alloyed with Au and/or Pd is especially preferred, and
electrolessly deposited catalyst has been found to possess superior
properties. The catalyst may also be in the u-bend.
The u-bend is preferably a simple u-bend 52, meaning that it is
unobstructed and contains an open, bulk flow for gas flow. The U
can be rounded or have corners. In some embodiments, the u-bend can
have baffles 55 (see FIG. 5b) or other structures that provide
additional surfaces for catalyst 54; however, the heat generating
channel(s) of the reactor should allow for fast flow of the process
stream. Thus, the oxidation side is preferably unobstructed (for
example, without felts, powders or other impediments to flow) and
contains a wall coating and a bulk flow path; in some preferred
embodiments, the product channel(s) are also unobstructed with a
wall coating and a bulk flow path.
In some preferred embodiments, the product channel (also called the
second section) has a larger cross-sectional area (and thus a
larger volume) than the process channel (also called the first
section). This provides additional contact time for the relatively
slower dehydrogenation process. Preferably, the process channel has
an essentially constant cross section that is the same size or
smaller than the product channel. The product channel can increase
in volume along its length (see an embodiment of this in FIG. 3 in
which shims are stepped to gradually increase volume). In some
preferred embodiments, the second section includes a
cross-sectional area that is at least two times (in some
embodiments at least 3 times and in some embodiments at least 5
times) larger than that of the first section. The length of the
first section and the second section can be the same or
different.
As exemplified in FIGS. 1 and 2, oxygen (or hydrogen) can be added
stagewise into the process stream as it passes through the first
section. Optimally, catalyst is disposed on the surface opposing
the oxygen jets so that the exothermic reaction occurs on the wall
for heat transfer to the cracking reaction. Oxygen should not be
added to the second section.
In scaled up apparatus with numerous channels, such as the
multichannel reactor of FIG. 1, there are flow equalizing
structures at the header connecting the microchannels with larger
piping. These structures, such as shown in FIG. 8, equalize flow to
plural channels throughout a device. Flow equalizing structures are
known in the art. In a preferred embodiment, there are no flow
equalizing structures on the footer of a multichannel device. More
preferably the reactor is operated in a vertical direction with
respect to gravity so that soot particles can more easily drop out
of the product channel.
Apparatus Design That Minimizes Heat Transfer to Exterior
FIG. 6 illustrates apparatus that minimizes heat transfer to the
exterior of a device. In this device, the device 60 has a central
axis 61 and flow paths 63 radiating from the central axis. The
device can be made by known processes such as stacking sheets to
form a laminated device or electro-discharge machining. An open
area 65 at the end of the flow paths can form a u-turn so that a
process stream returns in the direction it came. Also, as shown in
FIG. 6, numerous such devices can share a common manifold. In a
particularly preferred embodiment, plural devices can be plugged
into a single unit including both an inlet and an outlet to
accommodate flow to and from the plural devices. For chemical
reactions, it may be desirable for catalyst to be disposed in one
or more of the flow paths. For separation processes, may be
desirable for adsorbent to be disposed in one or more of the flow
paths. Also, as shown in FIG. 6, plural processor bodies can be
connected into a common manifold 66 with manifold inlet 67 and
manifold outlet 69.
Oxidative Dehydrogenation Reactions
This invention discloses methods for the oxidative dehydrogenation
of alkane(s) and/or aralkane(s) to alkene(s), alkadiene(s) and/or
aralkene(s). The hydrocarbon may be any alkane or aralkane of
C.sub.2 up to C.sub.20. Examples of alkane include ethane, propane,
isobutane or butane or higher alkanes including up to C.sub.20
linear and branched alkanes; examples of aralkane include
ethylbenzene; examples of alkene for the purpose of this invention
include ethylene, propylene and also alkadienes such as butadiene;
examples of aralkene include styrene. Preferred examples of
hydrocarbons are C.sub.2-C.sub.18 alkanes, preferably
C.sub.2-C.sub.10 alkanes, ethylbenzene, or C.sub.10-C.sub.15
alkanes such as could be used for making detergent alcohols.
Ethane, propane, butane and isobutane are especially preferred
hydrocarbons. The alkanes can be linear, branched and cyclic.
Hydrocarbons can be obtained commercially either in pure form or in
mixtures. Hydrocarbons can also be derived from other reactions,
and the output of these reactions used with or without an
intervening purification step.
In this method, a hydrocarbon-containing mixture (the mixture is or
contains a fluid and may be homogeneous or heterogeneous (for
example, containing some colloidal liquid droplets or solid
particulates)) flows past and/or through a catalyst material.
Preferably the mixture is entirely gaseous. The mixture comprises a
source of oxygen and at least one hydrocarbon; in preferred
embodiments, the oxygen source is introduced immediately before the
catalyst zone or within the reactor catalyst zone or, most
preferably, in a staged fashion along a length of a process
channel. A portion of the at least one hydrocarbon reacts to form
at least one alkene and/or aralkene and the source of oxygen reacts
to form water. The oxygen source is preferably dioxygen (O2), and
in some embodiments air is used to provide oxygen. Optionally, the
product stream can be rapidly quenched to preserve products and
stop further reaction to undesirable products. Quenching can be
achieved using integral microchannel quench/heat exchanger to
remove heat in adjacent channels to the channels through which the
product is flowing. In another embodiment, the quench can be
achieved by mixing the hot product stream with a cold fluid to
rapidly reduce temperature. The quench fluid can be condensible
fluids, for example, excess low temperature steam or a condensible
hydrocarbon injected as a liquid that evaporates and cools the
product stream by absorbing latent heat of evaporation from the hot
product stream. Condensible fluids are attractive for use in
commercial applications for gas-phase products, since they are
relatively easily separated from the product mixture.
Systems of the invention can be described as including apparatus
and/or catalyst in combination with reactants and/or products.
Additionally, any of the individual components (such as ethane, for
example) may preferably be present in at least 20% purity (based on
carbon atoms), or at least 50%, or at least 90%, or 100%
purity.
For autothermal ODH of an hydrocarbon (such as ethane) to an alkene
(such as ethylene) or aralkene, the ethane:H.sub.2 feed ratio is
preferably in the range 1:0 to 1:1.5; more preferably 1:0.2 to 1:1,
preferably 1:0.2 to 1:0.8, most preferably 1:0.5 to 1:0.8, and the
ethane:O2 feed ratio should remain in the range 1:0.1 to 1:1,
preferably 1:0.2 to 1:0.8 and most preferably 1:0.25 to 1:0.5
depending on the overall reaction selectivities and conversion.
Hydrogen in the process stream may be fed from a separate source or
produced in the ODH reaction and recycled.
The reactant stream may contain diluents such as nitrogen, methane,
water vapor, CO, and CO.sub.2. Steam, if present in the reactant
feed, is preferably present in a steam:C ratio of 5 or less, more
preferably 1 or less, and in some embodiments 2 volume % or less.
The total diluents to dehydrogenatable hydrocarbons molar ratio is
preferably 5:1 or less, more preferably 2:1 or less, preferably
less than 50 volume %, more preferably less than 20 volume %
diluents in a microchannel reactor, and in some embodiments, less
than 2 vol. % diluents. In some preferred embodiments, the
hydrocarbons in the reactant stream are at least 75 mol %, more
preferably at least 90 mol % of a single hydrocarbon (propane, for
example). In some preferred embodiments, the reaction stream
contains essentially no diluent.
In some embodiments of the inventive reactor or method, the reactor
(or method) is configured to send the product stream into a second
reactor or recycle the product stream back into the same reactor.
There may be intervening separation steps to remove desired
products or undesired components or separate hydrogen or a reactant
or reactants. In some preferred embodiments, separation is
conducted within the same integrated device as the dehydrogenation.
Typically, the desired alkene or arylalkene will be separated from
the product stream and the unreacted hydrocarbon portion of the
product stream recycled.
A product stream containing olefins and unconverted alkanes can be
used without further separation as a feedstock for other processes
including alkylation. In alkylation, (typically) olefins are
reacted with isoalkanes to form higher branched alkanes with high
octane numbers suitable for use as components of gasoline. Where
the feedstock contains isobutene, the product stream is especially
suited as an alkylation feedstock since the products include C3-C5
olefins and unconverted isobutane.
In some preferred embodiments, walls of the reaction channels
and/or inner surfaces of conduits and manifolds connected to the
reaction channels are coated with a passivation layer. Passivation
of surfaces inside the reaction chamber and/or in piping leading
to, and/or especially piping leading from the reaction chamber may
reduce coking and nonselective oxidation reactions and might
enhance time-on-stream performance. Passivation coatings have a
different composition than the underlying material. Suitable
passivation coatings include a refractory oxide such as silica,
alumina, zirconia, titania, chromia, ceria, Group II metals
(alkaline earths) and rare earth metals, atomic numbers 57-71. The
passivation coating could, optionally, be catalytic supports or
could be dense coatings to protect an underlying metal wall. It is
believed that surfaces may quench undesired gas phase unselective
oxidations. Thus, in some embodiments, filler material such as
ceramic fibers could be placed into the reaction channel in open
spaces within the reaction channel that, during operation, would be
occupied by hot gas.
The process channel contains an oxidative dehydrogenation catalyst.
In some preferred embodiments, there is an oxidative
dehydrogenation catalyst in both the process channel and the
product channel, and in some preferred embodiments, there is an
oxidative dehydrogenation catalyst in only the product channel.
Catalyst structures within the product channel may include porous
catalyst materials, monoliths, washcoats, pellets, and powders.
Electroless catalyst coatings on microchannel walls are especially
preferred.
In its broader aspects, a catalyst or catalysts that are known in
the prior art can be used in the apparatus of the present
invention. However, the ODH catalysts described above and in the
examples are particularly preferred.
If necessary, the catalyst systems can be regenerated by treating
the catalyst with an oxidant to oxidize reduced materials formed on
or in the catalyst. Typical regeneration oxidants are oxygen or
air. Catalysts can be refurbished after irreversible reduction of
activity by coating the catalyst in situ with additional active
materials.
In addition to the reaction microchannel(s), additional features
such as microchannel or non-microchannel heat exchangers may be
present. An integrated or separate heat exchanger can be used to
quench the reaction products, cooling them down rapidly once the
reaction has taken place to prevent further undesirable reactions
of the olefins. In some embodiments of the inventive reactor or
method, the reactor (or method) is configured to send the product
stream into a second reactor or recycle the product stream back
into the same reactor.
With microchannel reactors the high heat removal capacity makes it
possible to run reactions at higher pressures and high space
velocity in conventional reactors and still achieve high
selectivity at high conversion. With pressures above 2 atm,
preferably above 5 atm, and more preferably above 10 atm and space
velocities greater than 10,000 h-1, preferably greater than 100,000
h-1, and more preferably greater than 1,000,000 h-1 it is possible
to get good yields of useful products in microchannel reactors.
Preferred temperature ranges of the process of the present
invention include: above 850.degree. C.; a temperature ranging from
850 to 1050.degree. C., more preferably above 900-1050.degree. C.,
more preferably above 900.degree. C., and in some embodiments
950-1000.degree. C. Unless otherwise specified, "temperature" means
peak temperature in the device. Alternatively, the temperature
could be specified as temperature in a location such as the u-bend
or second section, or as average temperature.
For operation at these temperatures, it is desirable that the
internal surfaces of the reactor be covered with a passivation
layer.
In some preferred embodiments, the temperature increases
substantially monotonically along the length of the process channel
from the start of the exothermic oxidation to the u-bend (i.e., the
highest temperature is at the u-bend). "Monotonically" means in the
same direction, not at the same rate. Substantially monotonic
increases are shown in the examples.
Preferred pressures in the reactor are in the range of 0 to 20 bar,
more preferably 0 to 8 bars. Pressures are gauge unless specified
otherwise.
Gas hourly space velocity (GHSV) of the inventive methods
preferably range from 1,000 h.sup.-1 to 10,000,000 h.sup.-1 based
on reactor volume, or 1,000 ml feed/(g catalyst)(hr) to 10,000,000
ml feed/(g catalyst)(hr). In other preferred embodiments, GHSV is
at least 10,000 h.sup.-1 or at least 10,000 ml feed/(g
catalyst)(hr); more preferably at least 100,000 h.sup.-1 or at
least 100,000 ml feed/(g catalyst)(hr); more preferably at least
500,000 h.sup.-1 or at least 500,000 ml feed/g catalyst; more
preferably at least 1,000,000 h.sup.-1 or at least 1,000,000 ml
feed/(g catalyst)(hr). Liquid hourly space velocity (LHSV) is
preferably at least 5 h.sup.-1; more preferably at least 20
h.sup.-1; more preferably at least 60 h.sup.-1; more preferably at
least 100 h.sup.-1.
Contact times in the reaction chamber are preferably are in the
range of 0.001 to 5 s, more preferably less than 500 ms, more
preferably less than 100 ms, and still more preferably less than
about 70 ms. Volumes for determining contact times are reactor
volumes in which the conditions are sufficient for either an
oxidation or dehydrogenation reaction to occur; the volumes include
catalyst volume (typically this volume is insignificant for an
electroless plating). So, under typical ODH reaction conditions,
the volume for calculating contact time typically includes the
volumes of the first section, u-turn and second section. The volume
would not include sections of channels where only recuperation
(heat exchange) is occurring. Trivial amounts of reaction are
disregarded in calculating volume.
Preferably, selectivity to carbon oxides (on a carbon atom basis)
is less than 40%, more preferably less than 20%, and even more
preferably less than 5%, and in some embodiments in the range of
20% and 2%.
The percent conversion of hydrocarbon (in a single pass) is
preferably 50% or higher, more preferably about 60% or higher, more
preferably 70% or higher, even more preferably 80% or higher, and
in some embodiments in the range of 70 to about 86%. The level of
percent selectivity to desired product (or products in the case
where more than one valuable alkene can be formed) is preferably at
least 50% more preferably at least 70%, more preferably at least
80%, and in some embodiments 80 to about 86%.
Oxygen conversions are preferably greater than 90%, more preferably
greater than 95%, most prefereably greater than 99%.
EXAMPLES
Modeling Oxidative Dehydrogenation of Ethane in a Microchannel
Reactor Having a U-Bend Configuration
A microchannel reactor was designed to that utilized common
channels to perform hydrogen oxidation and ethane cracking. The
device was designed using a series of computational fluid dynamic
(CFD) simulations in order to achieve an expected performance of
78% ethane conversion and 84% ethylene selectivity by using a molar
feed ratio of approximately 4.5:4:1 ethane to hydrogen to oxygen,
corresponding to an overall device pressure drop of less than 25
PSI.
The multi-channel reactor design consists of eight identical
channel sets that each includes an inlet process channel, an inlet
oxygen channel and an outlet product channel (see FIG. 1). Each of
the eight inlet process channels has dimensions of width equal to
0.25'' and of gap equal to 0.010''. Each of the eight inlet oxygen
channels are subdivided into three sub-channels that overlaps and
combines with a single process channel. Each of the oxygen
sub-channels have dimensions of width equal to 0.03'' and of gap
(top to bottom height in the illustrated cross-section) equal to
0.010'' and are equally spaced across the 0.25'' wide process
channel (see FIG. 2). The oxygen is mixed into the process channels
by utilizing a staged addition process that uses a series of small
circular jets ranging in diameter from 0.006''-0.010''. By
controlling the oxygen addition and hence the heat release, the
thermal profile can be tailored to reduced internal stresses and
therefore increase the life of the reactors. The oxygen is staged
into the process channel over a length of 4.5'' and incorporates 7
circular jets, each separated by 0.75''. There is one set of seven
jets for each of the oxygen sub channels and therefore there are
twenty-one jets for each of the process channels. Approximately
0.5'' downstream of the last staged addition point, the process
channel transitions into the product channel by turning 180.degree.
through a 0.20'' u-turn feature. The product channel has a width
equal to 0.25'' is directly overlies a single process channel. Once
the gas flow has been turned (by passing through the u-turn), the
product channel transitions from a gap of 0.020'' up to 0.060'' by
going through a series of 0.010'' steps that are each 0.05'' long.
Transitioning in this manner allows the flow to expand and reduce
velocity without initiating any significant recirculation zones in
the flow field (see FIG. 3). The product flow is counter to the
process flow such that the heat generated from the hydrogen
oxidation in the process channel can pass into the product stream
to sustain the ethane cracking reaction (see FIG. 4). Once the
product stream fully passes the hydrogen oxidation section, it
passes heat to the process and oxygen channels along the length of
a counter flow heat exchanger in order to preheat the reactants and
cool the products (see FIG. 7). The product streams then exits
straight out of the bottom of the device.
The eight channel sets that make up the multi-channel reactors are
arranged by having four layers, each with two channel sets
side-by-side. The process stream is brought in through the side of
the device by four sub-manifold channels that each feed two side by
side process channels. Flow distribution features have been added
to ensure uniform distribution across the two channels (see FIG.
8). The oxygen stream is brought in through the side opposite from
the process stream, by four sub-manifold channels that each feed
six side-by-side oxygen sub channels. The flow distribution
features are identical for the oxygen and process streams and each
contains a 0.5'' wide by 0.020'' gap sub-manifold channel, a single
gate that spans the feed channels, and a single 0.375'' long by
0.010 gap redistribution zone that also spans the feed channels
(see FIG. 8).
The multi-channel reactors can be fabricated by stacking a series
of 0.010'' and 0.020'' thick shims between two 0.375'' endplates
and diffusion bonding them together. The shim sizes are .about.16''
by 16'' such that multiple reactors can be included in one shim
stack. The final bonded stack includes a total of nine devices laid
out side by side. After diffusion bonding these devices are cut
apart using wire EDM in order to separate the nine individual
multi-channel reactors. The process and oxygen sub-manifold
channels as well as the product exit channels can be opened up
using plunge EDM. The main headers and footers can be welded in
place. The reactor is then cleaned, aluminized, and heat treated.
The catalyst solution is applied through the manifolds.
Computational fluid dynamic (CFD) simulations were conducted to
determine the staged oxygen distribution, thermal profile,
predicted performance, and the sub-manifold to feed channel flow
distribution quality. Two different sets of CFD models were used in
these analyses. The first set of models represented a slice of the
entire reactor that included 9'' of heat exchange, 5'' of hydrogen
oxidation and 5'' of ethane cracking. The model domain included a
single 0.25'' wide by 0.010'' gap process channel, three 0.030''
wide by 0.010'' gap oxygen sub-channels, and a single 0.25'' wide
by 0.06'' product channel. The oxygen and process channels were
separated by a 0.010 thick shim that included a seven jet pattern
for each of the three oxygen sub-channels. The process and product
channels were separated by a 0.040'' thick shim that included a
0.25 wide by 0.020 gap u-turn feature. The product channel included
a small transition zone in which the channel gap was increased from
0.020'' to 0.060'' in 0.010'' steps. Each step was 0.050'' long.
The product channel was bounded with 0.02'' thick metal to created
one external face of the domain and the oxygen channel was bounded
by 0.020'' metal to create the opposite external face of the
domain. The external sides of the domain included 0.030'' metal to
fully enclose the channels and allow for axial conduction (see FIG.
9). The domain incorporated two types of thermal boundary
conditions. The external sides the domain incorporated adiabatic
boundary conditions and the external faces of the domain
incorporated a periodic boundary conditions that forced both of the
external domain faces to have identical temperature maps (see FIG.
9). A number of fully reactive cases were run using this type of
model in order to finalize the staged oxygen addition and then to
compare the predicted performance under a number of simulated
conditions. Each modeled run utilized a feed ratio of 4.5:4:1
(ethane:hydrogen:oxygen) but exit pressure was varied between one
atmosphere and three atmospheres and the total flow rate was varied
between 10 SLPM and 30 SLPM (where total flowrate includes all of
the feed gases for an entire multi-channel reactor containing eight
sets of channel sets).
The results of the simulations predict that the reactors will be
able to achieve the desired ethane conversion and ethylene
selectivity at the low flowrate cases (10 SLPM) and over an
operational pressure range of at least 0-30 PSIG. The performance
starts to suffer as the flowrate is increased. One of the reasons
that the performance is reduced is due to inefficient heat exchange
between the process and product streams (see table 1 and FIG. 10).
Although the total ethane conversion varied for each of the runs,
each simulation predicted the trend that .about.1/3 of the ethane
conversion occurred in the hydrogen oxidation zone (i.e. process
channel) and the remaining 2/3 of the conversion occurred in the
cracking zone (i.e product channel) (see FIG. 11). Furthermore, all
simulations predicted that 100% of the oxygen was converted in the
process channel prior to entering the u-turn. The maximum
temperature predicted varied per case although generally occurred
in the process channel just downstream of the last oxygen jet. The
maximum metal temperature is predicted to be within the
1025.degree. C.-1075.degree. C. range and is dependent on the
flowrate and operational pressure.
TABLE-US-00001 TABLE 1 Predicted Performance Outlet Total Flow
Pressure Ethane Ethylene Acetylene Carbon Rate (SLPM) (ATM)
Conversion Selectivity Selectivity Selectivity 10 1 74.7% 89.5%
1.5% 0.5% 10 2 74.2% 92.0% 0.9% 0.4% 20 2 71.2% 89.2% 1.0% 0.6%
A second geometry was modeled that was identical to first except
that the product channel was modified to include three 0.25'' wide
by 0.020'' gap channels separated by a 0.010'' thick shim instead
of the open 0.060'' product channel that was modeled in the first
simulation set (see FIG. 12). The process channel is shaded and the
flow paths in the product channel are black. The modification to
the product channel was done to allow more efficient heat exchange
between the process and product streams. Identical cases were run
to compare the two designs. The modified design showed more
efficient heat transfer and therefore outperformed the initial
design at the higher flowrate conditions (see table 2 and FIG. 13).
The ethane conversion and oxygen conversion showed similar trends
as the initial design.
TABLE-US-00002 TABLE 2 Predicted Performance Total Flow Outlet
Ethane Design Rate Pressure Con- Ethylene Acetylene Carbon Type
(SLPM) (ATM) version Selectivity Selectivity Selectivity Initial 10
1 74.7% 89.5% 1.5% 0.5% Initial 10 2 74.2% 92.0% 0.9% 0.4%
Testing of Various Pt Alloys in Microchannels for the Oxidative
Dehydrogenation of Ethane to Ethylene
Example 1
A coupon formed from a high temperature alloy coated with
Pt-aluminide was heat-treated at 1050.degree. C. for 10 hours prior
to use. The surface of the coupon was covered with an
.alpha.-Al.sub.2O.sub.3 scale. The coupon was then put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4.H.sub.2O. The plating was performed at
room temperature for 7 hours. The coupon was then cleaned with
deionized water and dried in air at room temperature. Subsequently
the coupon was put in a new Pt plating solution with the same
composition. The plating was performed at room temperature for
another 9 hours. The total Pt loading was 12 mg/in.sup.2. After the
plating, the coupon was calcined at 1000.degree. C. for 4 hours in
air.
The Pt plated coupon was tested in a microchannel reactor for
oxidative dehydrogenation of ethane to ethylene. The reactor has
two microchannels separated by the catalyst coupon. Reactants were
fed at 3:2:1 ratio of ethane:hydrogen:oxygen. Catalyst entrance
temperature ranged from 850 to 950.degree. C., and contact time was
fixed at 40 ms. Reaction products, i.e., ethylene, acetylene,
methane, C3 (propane and propylene), C4 (butylenes, butanes and
butadiene) and COx (CO and CO.sub.2), were analyzed with an on-line
four-column GC. The ODH performance is summarized in Table 1.
Example 2
A Pt-aluminide coupon was heat-treated at 1050.degree. C. for 10
hours prior to use. The surface of the coupon was covered with an
.alpha.-Al.sub.2O.sub.3 scale. The coupon was then put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4.H.sub.2O. The plating was performed at
room temperature for 7 hours. The Pt loading was 3.8 mg/in.sup.2.
Subsequently, the Pt-plated coupon was put in a Cu plating solution
with CuCl.sub.2 (0.4 wt % Cu), 0.6 wt % HCHO, 8 wt % Na.sub.4-EDTA.
The pH of the solution was adjusted to 12.3 by KOH. The plating was
performed at room temperature for 11 min. The Cu loading was 6.4
mg/in.sup.2 After the plating, the coupon was heat-treated at
900.degree. C. for 4 hours in flowing H.sub.2. A PtCu.sub.3 alloy
was formed (surface XRD analysis) after the heat-treatment.
The ODH performance is summarized in Table 1. Ethylene selectivity
is increased by 8%, from 75.5% to 83.5%, at around 77% ethane
conversion as compared to the Pt-plated catalyst.
Example 3
A Ni-aluminide coupon was heat-treated at 1050.degree. C. for 10
hours prior to use. The surface of the coupon was covered with an
.alpha.-Al.sub.2O.sub.3 scale. The coupon was then put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4.H.sub.2O. The plating was performed at
room temperature for 15 hours. The coupon was then cleaned with
deionized water and dried in air. Subsequently the coupon was put
in a new Pt plating solution with the same composition. The plating
was performed at room temperature for another 0.5 hour. The total
Pt loading was 8.3 mg/in.sup.2. Subsequently, the Pt-plated coupon
was put in an Au plating solution with KAu(CN).sub.2 (0.4 wt % Au),
0.4 wt % KCN, 1.0 wt % KOH, 2.5 wt % sodium citrate, 0.2 wt %
Na.sub.4-EDTA, Pb(CH.sub.3COO).sub.2 (2 ppm Pb) and 1 wt %
dimethylamine borane. The plating was performed at 80.degree. C.
for 2 hours. The Au loading was 4.2 mg/in.sup.2. After the plating,
the coupon was heat-treated at 900.degree. C. for 4 hours in
flowing H.sub.2.
The ODH performance is summarized in Table 1. As compared to the
Pt-plated catalyst, ethylene selectivity is increased by 6.7%, from
75.2% to 81.9%, at around 78.6% ethane conversion. Also no apparent
deactivation was seen in 100-h on stream.
Example 4
A Ni-aluminide coupon was heat-treated at 1050.degree. C. for 10
hours prior to use. The surface of the coupon was covered with an
.alpha.-Al.sub.2O.sub.3 scale. The coupon was then put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4.H.sub.2O. The plating was performed at
room temperature for 20 hours. The Pt loading was 8.1 mg/in.sup.2.
Subsequently, the Pt-plated coupon was put in a Pd plating solution
with 0.9 wt % PdCl.sub.2, 3.4 wt % (NH.sub.4).sub.2H.sub.2-EDTA, 10
wt % NH.sub.4OH and 0.3 wt % N.sub.2H.sub.4.H.sub.2O. The plating
was performed at room temperature for 23 min. The Pd loading was
4.4 mg/in.sup.2. After the plating, the coupon was heat-treated at
900.degree. C. for 4 hours in flowing H.sub.2.
The ODH performance is summarized in Table 1. As compared to the
Pt-plated catalyst, ethylene selectivity is increased by 7.4%, from
75.6% to 83%, at around 77% ethane conversion.
Example 5
A Ni-aluminide coupon was heat-treated at 1050.degree. C. for 10
hours prior to use. The surface of the coupon was covered with an
.alpha.-Al.sub.2O.sub.3 scale. The coupon was then put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4.H.sub.2O. The plating was performed at
room temperature for 7.4 hours. The Pt loading was 5.0 mg/in.sup.2.
Subsequently, the Pt-plated coupon was put in a Pd plating solution
with 0.9 wt % PdCl.sub.2, 3.4 wt % (NH.sub.4).sub.2H.sub.2-EDTA, 10
wt % NH.sub.4OH and 0.3 wt % N.sub.2H.sub.4.H.sub.2O. The plating
was performed at room temperature for 11 min. The Pd loading was
2.9 mg/in.sup.2. After that, the Pt--Pd plated coupon was put in an
Au plating solution with KAu(CN).sub.2 (0.4 wt % Au), 0.4 wt % KCN,
1.0 wt % KOH, 2.5 wt % sodium citrate, 0.2 wt % Na.sub.4-EDTA,
Pb(CH.sub.3COO).sub.2 (2 ppm Pb) and 1 wt % dimethylamine borane.
The plating was performed at 80.degree. C. for 26 min. The Au
loading was 7.0 mg/in.sup.2. After the plating, the coupon was
heat-treated at 900.degree. C. for 4 hours in flowing H.sub.2.
The ODH performance is summarized in Table 1. As compared to the
Pt-plated catalyst, ethylene selectivity is increased by 7.3%, from
75.6% to 82.9%, at around 77% ethane conversion. Also no apparent
deactivation is seen in 50 hours on stream.
Example 6
A Ni-aluminide coupon was heat-treated at 1050.degree. C. for 10
hours prior to use. The surface of the coupon was covered with an
.alpha.-Al.sub.2O.sub.3 scale. The coupon was then put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4.H.sub.2O. The plating was performed at
room temperature for 22 hours. The Pt loading was 8.9 mg/in.sup.2.
The coupon was then cleaned with deionized water and dried in air
at room temperature. Subsequently the coupon was put in a new Pt
plating solution with the same composition. The plating was
performed at room temperature for another 1.5 hours. The total Pt
loading was 11 mg/in.sup.2 Next, the Pt-plated coupon was put in a
Pd plating solution with 0.9 wt % PdCl.sub.2, 3.4 wt %
(NH.sub.4).sub.2H.sub.2-EDTA, 10 wt % NH.sub.4OH and 0.3 wt %
N.sub.2H.sub.4.H.sub.2O. The plating was performed at room
temperature for 5 min. The Pd loading was 2.5 mg/in.sup.2. After
the plating, the coupon was heat-treated at 900.degree. C. for 4
hours in flowing H.sub.2.
The ODH performance is summarized in Table 1. As compared to the
Pt-plated catalyst, ethylene selectivity is increased by 3.7%, from
75.6% to 79.3%, at around 78% ethane conversion.
Example 7
A Ni-aluminide coupon was heat-treated at 1050.degree. C. for 10
hours prior to use. The surface of the coupon was covered with an
.alpha.-Al.sub.2O.sub.3 scale. The coupon was then put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4.H.sub.2O. The plating was performed at
room temperature for 7 hours. The Pt loading was 5.0 mg/in.sup.2.
Subsequently, the Pt-plated coupon was put in an Au plating
solution with KAu(CN).sub.2 (0.4 wt % Au), 0.4 wt % KCN, 1.0 wt %
KOH, 2.5 wt % sodium citrate, 0.2 wt % Na.sub.4-EDTA,
Pb(CH.sub.3COO).sub.2 (2 ppm Pb) and 1 wt % dimethylamine borane.
The plating was performed at 80.degree. C. for 1 hour. The Au
loading was 8.0 mg/in.sup.2. After the plating, the coupon was
heat-treated at 900.degree. C. for 4 hours in flowing H.sub.2.
The ODH performance is summarized in Table 1. As compared to the
Pt-plated catalyst, ethylene selectivity is increased by 4.6%, from
75.6% to 80.2%, at around 77% ethane conversion.
TABLE-US-00003 TABLE 1 ODH performance of electroless plated
Pt-alloy catalysts Con- version (%) Selectivity (%) C balance
Example Catalyst T (.degree. C.) C.sub.2H.sub.6 O.sub.2
C.sub.2H.sub.4 CH.sub.4 COx C.sub.2H.sub.2 C3 - C4 (%) 1 Pt on PtAl
850 71.3 94.9 76.2 7.3 11.8 0.6 2.4 1.7 -0.8 12 mg/in.sup.2 865
76.5 95.2 75.6 7.7 11.9 0.9 2.1 1.8 -1.9 875 78.7 96.5 75.2 7.8
12.0 1.1 2.0 1.9 -0.6 885 82.7 96.8 73.7 8.4 12.1 1.5 1.8 2.1 -1.2
2 Pt--Cu (1:5) on PtAl 890 72.6 99.6 85.1 5.1 4.2 1.7 1.5 2.3 0.5
10 mg/in.sup.2 902 77.4 99.8 83.6 5.4 4.2 2.3 1.5 3.0 0.7 910 80.7
99.5 82.4 5.8 4.0 2.8 1.4 3.7 0.2 3 Pt--Au (2:1) on NiAl 890 66.5
98.7 83.1 5.3 6.7 1.2 1.7 2.0 0.4 12.5 mg/in.sup.2 905 73.8 99.2
82.1 5.9 6.0 1.8 1.6 2.6 0.7 915 78.6 99.4 81.9 6.1 4.7 2.5 1.5 3.3
-4.2 930 86.5 99.4 78.3 7.1 4.2 3.8 1.3 5.3 -3.1 4 Pt--Pd (1:1) on
NiAl 910 66.3 99.7 85.6 4.3 3.7 2.5 1.6 2.3 -3.0 12.5 mg/in.sup.2
930 77.0 99.7 83.0 5.2 3.4 3.5 1.5 3.4 -3.0 940 82.0 99.8 81.3 5.8
3.3 4.2 1.5 3.9 -3.8 5 Pt--Pd--Au (1:1:1.4) on NiAl 925 59.8 99.8
86.1 4.5 3.3 2.3 1.4 2.4 0.9 14.9 mg/in.sup.2 928 77.5 100.0 82.9
5.1 2.2 4.1 1.4 4.3 0.9 935 80.1 99.8 81.7 5.4 2.2 4.5 1.4 4.8 1.0
950 85.1 99.8 79.1 6.0 2.0 5.5 1.3 6.1 1.5 6 Pt--Pd (5:1) on NiAl
865 61.6 97.4 81.3 5.7 9.1 0.4 1.9 1.6 -2.6 13.5 mg/in.sup.2 875
65.2 98.5 81.8 5.8 8.1 0.7 1.8 1.8 -1.6 900 78.4 99.1 79.3 7.1 7.5
1.8 1.6 2.7 -1.6 915 83.8 99.3 77.4 7.7 7.6 2.4 1.4 3.5 0.7 7
Pt--Au (0.6:1) on NiAl 865 68.5 96.6 82.4 5.9 7.8 0.9 1.9 1.1 1.0
13 mg/in.sup.2 875 73.2 97.3 81.2 6.3 8.1 1.2 1.8 1.4 0.8 885 77.4
98.5 80.2 6.6 8.1 1.5 1.7 1.8 0.5 895 80.9 99.1 79.1 6.9 8.0 2.0
1.6 2.4 0.4 Reaction conditions: 3:2:1 ratio of
ethane:hydrogen:oxygen, and 40 ms contact time.
* * * * *